diff --git a/api/current.txt b/api/current.txt
index f3f1cb928934f8f0ab1a0de1801708cfaed81c30..f7053b62184d2fc06304fe1b8531ab11103a0b32 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -35016,11 +35016,12 @@ package android.os {
     method public boolean isIgnoringBatteryOptimizations(String);
     method public boolean isInteractive();
     method public boolean isPowerSaveMode();
+    method public boolean isRebootingUserspaceSupported();
     method @Deprecated public boolean isScreenOn();
     method public boolean isSustainedPerformanceModeSupported();
     method public boolean isWakeLockLevelSupported(int);
     method public android.os.PowerManager.WakeLock newWakeLock(int, String);
-    method public void reboot(String);
+    method public void reboot(@Nullable String);
     method public void removeThermalStatusListener(@NonNull android.os.PowerManager.OnThermalStatusChangedListener);
     field public static final int ACQUIRE_CAUSES_WAKEUP = 268435456; // 0x10000000
     field public static final String ACTION_DEVICE_IDLE_MODE_CHANGED = "android.os.action.DEVICE_IDLE_MODE_CHANGED";
diff --git a/api/system-current.txt b/api/system-current.txt
index e539e6cc60f62f08f36dd1283e678b5329f229e0..fe7b3999d7b7f3badf83c8379d0086230593efa4 100755
--- a/api/system-current.txt
+++ b/api/system-current.txt
@@ -5986,6 +5986,7 @@ package android.os {
     method @RequiresPermission(anyOf={android.Manifest.permission.DEVICE_POWER, android.Manifest.permission.USER_ACTIVITY}) public void userActivity(long, int, int);
     field public static final int POWER_SAVE_MODE_TRIGGER_DYNAMIC = 1; // 0x1
     field public static final int POWER_SAVE_MODE_TRIGGER_PERCENTAGE = 0; // 0x0
+    field public static final String REBOOT_USERSPACE = "userspace";
     field public static final int USER_ACTIVITY_EVENT_ACCESSIBILITY = 3; // 0x3
     field public static final int USER_ACTIVITY_EVENT_BUTTON = 1; // 0x1
     field public static final int USER_ACTIVITY_EVENT_OTHER = 0; // 0x0
diff --git a/core/java/android/os/PowerManager.java b/core/java/android/os/PowerManager.java
index ab4d424ac0532b17f899d52b1b9270a34742beb7..c618dbc2b551542d4e403e2a28baf6ccfceee0fc 100644
--- a/core/java/android/os/PowerManager.java
+++ b/core/java/android/os/PowerManager.java
@@ -20,6 +20,7 @@ import android.Manifest.permission;
 import android.annotation.CallbackExecutor;
 import android.annotation.IntDef;
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.annotation.RequiresPermission;
 import android.annotation.SdkConstant;
 import android.annotation.SystemApi;
@@ -604,6 +605,13 @@ public final class PowerManager {
      */
     public static final String REBOOT_SAFE_MODE = "safemode";
 
+    /**
+     * The 'reason' value used for rebooting userspace.
+     * @hide
+     */
+    @SystemApi
+    public static final String REBOOT_USERSPACE = "userspace";
+
     /**
      * The 'reason' value used when rebooting the device without turning on the screen.
      * @hide
@@ -1382,6 +1390,14 @@ public final class PowerManager {
         }
     }
 
+    /**
+     * Returns {@code true} if this device supports rebooting userspace.
+     */
+    // TODO(b/138605180): add link to documentation once it's ready.
+    public boolean isRebootingUserspaceSupported() {
+        return SystemProperties.getBoolean("ro.init.userspace_reboot.is_supported", false);
+    }
+
     /**
      * Reboot the device.  Will not return if the reboot is successful.
      * <p>
@@ -1390,8 +1406,14 @@ public final class PowerManager {
      *
      * @param reason code to pass to the kernel (e.g., "recovery") to
      *               request special boot modes, or null.
+     * @throws UnsupportedOperationException if userspace reboot was requested on a device that
+     *                                       doesn't support it.
      */
-    public void reboot(String reason) {
+    public void reboot(@Nullable String reason) {
+        if (REBOOT_USERSPACE.equals(reason) && !isRebootingUserspaceSupported()) {
+            throw new UnsupportedOperationException(
+                    "Attempted userspace reboot on a device that doesn't support it");
+        }
         try {
             mService.reboot(false, reason, true);
         } catch (RemoteException e) {
diff --git a/core/tests/coretests/src/android/os/PowerManagerTest.java b/core/tests/coretests/src/android/os/PowerManagerTest.java
index 576ac73bc183126f68e29c9dc6a71cde41b32cda..5cb7852f7acc75fcaff7567794267d8d3fbfd2d8 100644
--- a/core/tests/coretests/src/android/os/PowerManagerTest.java
+++ b/core/tests/coretests/src/android/os/PowerManagerTest.java
@@ -239,4 +239,17 @@ public class PowerManagerTest extends AndroidTestCase {
         verify(mListener2, timeout(CALLBACK_TIMEOUT_MILLI_SEC)
                 .times(1)).onThermalStatusChanged(status);
     }
+
+    @Test
+    public void testUserspaceRebootNotSupported_throwsUnsupportedOperationException() {
+        // Can't use assumption framework with AndroidTestCase :(
+        if (mPm.isRebootingUserspaceSupported()) {
+            return;
+        }
+        try {
+            mPm.reboot(PowerManager.REBOOT_USERSPACE);
+            fail("UnsupportedOperationException not thrown");
+        } catch (UnsupportedOperationException expected) {
+        }
+    }
 }